Many orthopedic implants are made of vanadium steel, stainless steel, cobalt alloys, titanium, gold and amalgams (a metal alloy containing mercury). For neural implants, silicon is most widely used.
A healing response that follows an implantation, impacts the long-term functionality of the implanted device. The prolonged healing process recruits a variety of body fluids, proteins, and unwanted cell types to the tissue-implant interface. Healing characteristics common to unsuccessful bone and neural prosthetic wound-healing include prolonged fibrous encapsulation and chronic inflammation.
Extensive scar tissue formation is a common occurrence that leads to implant failure for an orthopedic implant juxtaposed to bone or a neural implant with the conductive neural tissue. With regard to orthopedic implants, fibrous encapsulation (or callus formation) at the tissue-implant interface decreases the effectiveness of the implant's bonding to bone and often results in clinical failures. With regard to neural implants, glial scar-tissue forms around probes implanted into the central nervous system. The glial scar response, gliosis, includes the formation of cells, for example astrocytes, which encapsulate the probes with non conductive tissue. Gliosis inhibits the ability of the probes or any other implants to properly interact with the surrounding neural tissue.